Gearboxes and gear arrangements are utilised in a wide range of situations in order to couple drive mechanisms. Traditionally, gearboxes have been formed from gear wheels having appropriate teeth numbers and sizes to provide a desired gear ratio. However, such gearboxes have a number of disadvantages. Firstly, they require the use of lubricating oils, which may act as contaminants or fire hazards and may prove ineffective in hot or cold environments, where the oil viscosity varies, or in a low pressure environment, where the oil may evaporate. Furthermore, gearboxes based on gear wheels may be noisy, making them unacceptable for low noise environments such as in hospitals, libraries and residential areas, or for clandestine military activities.
More recently, magnetic gearboxes have been provided which comprise respective gear rotors with interpoles between them. The rotors incorporate permanent magnets, and the interpoles act to modulate the magnetic flux transferred between the gear rotors. Such magnetic gearboxes enable a speed-changing mechanical device to be provided in which there is no mechanical contact between input and output shafts, thus avoiding many of the problems of noise and wear that arise in gearboxes having contacting moving parts.
FIG. 1 shows a schematic cross-sectional view of a magnetic gear arrangement of the prior art. The magnetic gear arrangement 600 is an epicyclic gearbox and comprises an inner rotor 602 and an outer rotor 606. Permanent magnets providing respective pole pairs 604, 608 are fixed to the inner and outer rotors 602, 606, the opposite polarities of each permanent magnet being respectively indicated by dark and light shading. The permanent magnets affixed to the inner rotor 602 have alternating polarity along the circumference of the rotor. Similarly, the permanent magnets affixed to the outer rotor 606 have alternating polarity along the circumference of that rotor. Typically, one rotor is mechanically coupled to a drive mechanism and the other rotor is mechanically coupled to a driven mechanism.
The inner and outer rotors 602, 606 have different numbers of pole pairs 604, 608. Typically, the number of pole pairs of the outer rotor 606 is greater than the number of pole pairs of the inner rotor 602.
Pole elements 610 are provided between the inner rotor 602 and the outer rotor 606 and form an array to provide a coupling element having a cylindrical shape.
Each pole element 610 forms one interpole for modulating the magnetic fields produced by the inner rotor 602 and the outer rotor 606, so as to couple the two fields and hence the motion of the rotors. The angular position of the interpoles is a factor in determining the gearing of the magnetic gearbox.
The motion of the rotors 602, 606 may be either co-rotational or counter-rotational, depending on the number of magnets affixed to each rotor and the angular position/number of interpoles.
WO 2007/135360 discusses a variety of magnetic gear arrangements.